(a) Fields of the Invention
The present invention relates to optical devices such as solid-state image sensing devices, light receiving devices used for optical pickup systems, and hologram units, and to methods for fabricating such a device.
(b) Description of Related Art
In recent years, optical devices built in camcorders, digital cameras, digital still cameras, and the like have been provided in a package form produced in such a manner that an image sensing element such as a CCD is mounted on an adapter component such as a base of an insulating material and that the mounted image sensing element is packaged with its light receiving region covered with a translucent plate.
In order to downsize an optical device, an image sensing element remaining in a bare chip form is mounted on an adapter component such as a base (see, for example, Japanese Unexamined Patent Publication No. 2000-58805).
FIG. 7 is a sectional view showing the structure of a known optical device. Referring to FIG. 7, the optical device includes, as main components, a base 131 of frame shape, an image sensing element 135, and a translucent plate 136. The base 131 is made of ceramic or plastic resin and has an opening 132 in its center portion. The image sensing element 135 is formed of, for example, a CCD and attached to the lower surface of the base 131. The translucent plate 136 is made of glass and attached to the upper surface of the base 131 so that the plate faces the image sensing element 135 with the opening 132 interposed therebetween.
A region of the lower surface of the base 131 located along the edge of the opening 132 is formed with a recess 133, and wires 134 of a gold plated layer are each provided to extend from the vicinity of the opening 132 on the lower surface of the base 131 to the outside surface of the base 131. The image sensing element 135 is attached to a region of the lower surface of the base 131 located on the inner edge of the recess 133, and the element is disposed so that a light receiving region 135a thereof is exposed in the opening 132.
A portion of the upper surface of the image sensing element 135 located around its perimeter is provided with electrode pads (not shown) for sending and receiving signals between the image sensing element 135 and external equipment. An end of each wire 134 adjacent to the opening 132 is formed with an internal terminal portion. The internal terminal portion of each wire 134 and the corresponding electrode pad are electrically connected to each other with a bump (protruding electrode) 138 interposed therebetween. On the lower surface of the base 131, the image sensing element 135, the wires 134, and the bumps 138 are hermetically sealed with a sealing resin 137 provided around the image sensing element 135.
As shown above, the light receiving region 135a of the image sensing element 135 is disposed within a closed space formed together with the opening 132. The optical device thus constructed is mounted on a circuit board with the translucent plate 136 directed upward as shown in FIG. 7. A portion of each wire 134 located outside the recess 133 and on the bottom of the base 131 is formed with an external terminal portion, which is used for connection to an electrode on the circuit board.
Although not shown in FIG. 7, a lens barrel with an optical imaging system incorporated therein is fixed above the translucent plate 136. The positional relation between the lens barrel and the light receiving region 135a has a defined accuracy required to fall within a predetermined tolerance.
Then, through the optical imaging system incorporated in the lens barrel, light from an imaged object is concentrated on the light receiving region 135a of the image sensing element 135. The concentrated light is converted into electricity by the image sensing element 135.
Also, another exemplary optical device has been known which uses a base unlike the base 131 shown in FIG. 7, having the shape of a totally flat plate. The base does not have the recess 133 formed in its surface on which the image sensing element 135 is mounted (see, for example, Japanese Unexamined Patent Publication No. 2002-43554). In such a case, the external terminal portions arranged around the perimeter of the base bottom and positioned off the edge of the opening are connected to the electrodes on, the circuit board through great-diameter solder balls or the like, respectively. The solder balls adjust the gap between the lower surface of the image sensing element and the upper surface of the circuit board.
The solid-state image sensing device having the structure as described above provides a small package height and a small footprint, and is suitable for implementation with high packing density.
In addition, basically the same structure is applied also to optical devices such as light receiving devices for use in optical pickup systems for writing information in, reading information from, and rewriting information in a media including a DVD, a CD, and an MD, and hologram units integrating multiple components in an optical pickup.